1. Field of the Invention
The invention relates to new and useful improvements in the field of induction and exhaust manifolds used in internal combustion reciprocating piston engines and in particular to those types of engines which employ cylinder side-ports.
The invention presents new and useful applications of the ejector principle in the ventillation of reciprocating piston driven engines and in particular to those types of engines employing bottom-cycle manifolding used to conduct combustion gases from side-ports in the engine cylinder during the exhaust cycle and to provide a method of inducting fresh air into the engine cylinder through the same side-port and supplementary ports on the subsequent induction cycle.
2. Description of Prior Art
The principle of the ejector was first conceived in the early part of this century in Europe by LeBanc and in England by Parsons who are credited with the initial development. Applications of these principles were not introduced into the United States until 1915 when Harold M. Graham working in conjunction with the United States Government provided significant imporvements in design and efficiency over the previous English and European designs. The invention presented is an application of these principles to the combustion gas exhaust and air induction streams of the internal combustion engine.
In the invention presented a high velocity exhaust fluid stream impinges upon an intervening low velocity air effluent stream within a common receiver resulting in the transfer of energy from the high velocity exhaust stream to the low velocity air stream. Impact between the particles comprising the gaseous media of each stream causes a resultant vector change in the momenta of the sum total of reacting particles in a manner which directs the flow of each stream along a common path and thus induces a directed flow toward ducting provided for this purpose. On the subsequent induction stroke air from the common receiver is inducted into the engine cylinder for cooling the piston crown and other engine components and also supplies additional air to support combustion. Unlike previous designs of earlier inventions valves are not required at the side-port to separate the flow of exhaust gases and air during their respected exhaust and induction cycles.
Ejectors, aspirators and syphons belong to a family of flow inducting mechanism which operate on the principle of momentum exchange based on Newtons second law. However, the flow in the latter two types of mechanism is based on liquid fluids while ejectors are in most instances designed to accommodate the flow of gaseous fluids. The earliest development of liquid momentum exchange devices is credited to James Thompson about 1852 and by Rankine in 1870. Because of the disproportionate difference in the mass of liquids compared to gases the internal flow paths of liquid momentum exchange devices are most likely to be parallel so as to take advantage of the highest flow inertia. Also because liquids are viscous and have higher surface tensions the entrainment process is, therefore, more effective at the common boundary when the flow is parallel. However, in the invention presented the reacting streams are gaseous and the efficiency of the induction of air into the engine cylinder is seen to be highest when the air flow is also parallel or nearly parallel but moving in a counter current direction to that of the exhaust streams.
The invention presented is based on the classical design features of the ejector which is defined as a nozzle or jet whose flow is directed into a diffuser. In this respect a nozzle is defined as "any channel designed to increase fluid velocity and reduce pressure", while a diffuser is defined as, "any channel designed to reduce velocity and increase pressure". In this regard a freely expanding jet may be viewed as a nozzle. The earliest attempts of attaining bidirectional flow through side-ports in the engine cylinder were by Groth in 1937, U.S. Pat. No. 2,123,302. However, this system did not employ an ejector as defined above and the flow of the exhaust and air streams were parallel and in the same direction, characteristic of momentum exchange devices which employ liquid fluids as previously described. Pumping efficiency without the use of a nozzle and diffuser section, comprising an ejector, as previously described, is very low and the 180.degree. turning angle losses required for return air flow to the side-port in the parallel flowing system are too high for effective operation. In the present invention these deficiencies are corrected by the use of an ejector for efficient pumping action, and the air flow to the common receiver is in a nearly countercurrent direction which greatly reduces turning losses.
Other types of apparatus used principally in secondary combustion applications employ the use of venturis which operate on the Bernoulli principle which is quite different than the momentum transfer devices previously described. The first use of venturis in combustion gas streams was in the secondary combustion of blast furnace exhaust gas streams prior to 1955. These principles were then applied to the internal combustion engine by Hraboweckyj in 1969, U.S. Pat. No. 3,468,124. However, in this instance flow was unidirectional flowing only in the exhaust direction. Venturis are not ideally suited for bidirectional non-steady flow as encountered in the exhaust circuits of engine systems which operate on the Otto or Diesel thermodynamic cycles. Therefore, venturi applications should not be confused with the present invention which is designed to operate as an ejector.
Originally ejector designs were based on unidirectional steady-flow conditions. In the present invention the flow through the nozzle portion of the ejector is bidirectional and the resulting alternating flow is of varying pressure magnitude. Under these conditions the reduction of stream frictional losses and time dependent inertial turning conditions are of utmost importance in the design in order that the system function effectively in a practical sense. Therefore, the direction of flow in the air circuit is directed toward the side-port which greatly reduces these losses.
Exhaust gas flow from the engine side-port or nozzle occurs at critical or near critical pressure conditions while return air flow to the engine through the same side-port is accomplished under less vigorous ideal pressure conditions. In order to induct more air into the engine cylinder under the lower pressure conditions additional air induction holes are added horizontally to the engine cylinder at a position slightly below the exhaust nozzle.
The invention operates in the following manner. During the expansion stroke the piston uncovers the top exhaust side-port in the cylinder and gases flowing from the side-port flow into a nozzle or jet whose flow is directed toward a diffuser. The momentum exchange of the high velocity gases jetting from the side-port is used to entrain air from a surrounding common air receiver. Fresh air is pulled into the area as a result of the ejector action and the flow of this air is contiquous to the side-ports such that on the subsequent induction it is taken into the cylinder. It should be noted also, that some air is also taken in at the end of the exhaust blowdown process as a result of inertial flow which causes the cylinder pressure to drop below the air receiver pressure. In the operation of two-stroke engines the air contiguous to the cylinder side-ports is pressurized simultaneously by the inertial flow in the air duct and the returning compression wave in the exhaust duct during the momentary closure of the side-port by a protrusion on the piston face. However, when the exhaust duct is not tuned an external pressurizing source is required.
There are many energy saving advantages in the application of this type of manifold in the design of internal combustion engines. The advantages are seen to be in the lower thermal loads on the upper cylinder components as a result of the early exit of hot gases, and in the additional breathing capacity which increases the system volumetric efficiency. As a result of the early evacuation of exhaust gases the exhaust pumping losses are also reduced which is another feature of the design.
Therefore a novel feature of the invention is its ability to selectively separate the flow of air and combustion gases from a common air receiver volume for entry and exit from the engine cylinder without the use of valves. Another novel feature of the invention is the application of ejector design principles to non-steady state flow conditions with reversing bidirectional flow at the jet leading to and from the engine cylinder. These features coupled with the combination of jet and diffuser configurations and their sequential operation with the upper cylinder manifolding constitute the major design considerations of the invention but are not limited entirely to these.